Let $S \xrightarrow{\varphi} T$ be a mapping of sets. Prove that $\varphi$ is a monomorphism if and only if $\varphi^{-1}[\varphi[A]]=A$ for every subset $A$ of $S$. Prove that $\varphi$ is an epimorphism if and only if $\varphi\left[\varphi^{-1}[B]\right]=B$ for every subset $B$ of $T$.